1. Field of the Invention
This invention relates to a method of forming a piling structure using a locking bar, and to a piling structure formed by this method. The invention has particular application to piling which has a relatively high rigidity, but it is not limited to high rigidity piling.
2. Description of the Related Art
High rigidity piling has, in plan view, the appearance of a series of hollow boxes or sections. This is in contrast to ordinary piling which is in the form of sheets. The hollow boxes or sections are formed of individual steel structural members, for example I-sections, U-sections or angles, which are connected together along adjoining flanges by means of a locking bar. The locking bar includes a pair of opposing recesses for the flanges of adjoining structural members, these recesses narrowing towards the outside. Conventionally, the edges of the flanges of the structural members have lips formed thereon for engagement in the recesses of the locking bar. Such lips are formed during the hot rolling process in which the structural members themselves are formed, but there are difficulties with the lip forming process which tends to significantly increase the costs of producing the structural members.
Another problem with conventional high rigidity piling is that after each structural member is slotted together with the locking bars--in the case of an I-beam a locking bar is fitted on each of the flanges on one side--the member and bars must be welded together in order to create a homogenous profile to the piling and so that the full section modulus is developed. Furthermore, the structural members and locking bars need to be connected together so that they are carried integrally down into the ground during pile driving. The welding process is usually carried out at the production site, rather than the piling site, but it is labour intensive, slow, costly and can also lead to distortion of the structural members due to the high local heat levels used.
The problem of forming lips on the structural members has been solved in DE-C-593825 and EP-B-0072118. According to these patents, portions of the edges of the flanges of the structural members are deformed out of the plane of the remainder of the flange, such portions alternating with portions which are not deformed. Such deformed portions are generally known as "crimps", since the process by which they are usually formed in analogous to crimping. In end view, the edge of the flange has an outwardly tapered shape (in the manner of a "fish tail") and thus the edge can slot longitudinally in to one of the recesses of the locking bar, but cannot be pulled out laterally.
However, even with the crimped structural members, welding to the locking bar must still be done and therefore the second problem mentioned above still remains.